Depends on how mush demo is involved. If you do the demo and prep it can save you $$ but first find a person to weld and ask what they want $$ wise and then ask if they will be ok with you doing prep. Do what they say to the level they want it done and that should result in an acceptable repair. As to procedure (where to have lap joints, how to seal between layers, etc)that is what you need to work out with them. also be aware that in most (99%) of this type of repair there is NO warranty, so the more time/care you put into prep and post work, the better chance of a lasting repair.